Spanish cyclist Maria Isabel Moreno has become the first athlete to fail a drugs test at the Beijing Olympics.
Moreno, who was entered for the women's road race and individual time trial, tested positive for the endurance-boosting drug EPO.
She could now face a two-year ban and, under a new International Olympic Committee rule, could also be banned from the 2012 London Olympics.
The IOC said it expected up to 40 positive drug tests during the Games.
The Spanish cyclist, also known as Maribel Moreno, was tested on 31 July and left the city before the Games began.
"She was quite different after being tested," secretary general of the Spanish Cycling Federation Eugenio Bermudez said.
"She was crying all the time and she insisted she wanted to go home."
Reports in Spain had earlier said the cyclist had pulled out after suffering an "anxiety attack".
A statement on the cyclist's official website posted on Saturday said Moreno was in Spain recovering from "a strong anxiety attack suffered in the athletes' village".
Anyone involved will get the maximum punishment
Spain's sports minister Jaime Lissavetzky
"Even though her state of health is good she does not feel ready to justify or explain her reasons for leaving the village," the statement said.
Spain's government insisted it would take the strongest action possible to eradicate the problem.
"We are going to hunt down these shameless people who harm our athletes. We are going to clamp down totally and will take the toughest action," said Spain's sports minister Jaime Lissavetzky.
"I ask you Maribel, looking you in the eyes, 'who gave you the substance and where did you buy it?'
"Anyone involved will get the maximum punishment. We will find out who supplied the substances and, if necessary, jail them."
The Spanish Olympic Committee (SOC) said it was unaware of the positive test until being informed on Monday.
"This is a stain on Spanish sport," said SOC chief Alejandro Blanco said.
Seven Russian athletes were last week provisionally suspended by the IAAF for doping offences, but they had yet to arrive at the Games.